I think there is some evidence in 2 Corinthians that Paul used the word Christ to describe [Jesus] and that the nomen sacrum Chi-Sigma overline (with different endings according to case) was used to abbreviate Christ.
2 Corinthians 1.21-22:
1.21 But it is God who establishes us with you in [Christ], and has anointed us; 22 he has put his seal upon us and given us his Spirit in our hearts as a guarantee.
In this case, Paul is using the metaphor of anointing to refer to the reception of the Holy Spirit through Baptism. Why that metaphor? Because he has just referred to [Christ] the anointed one (and in v. 19 preceding as well). It might be necessary to go outside of Paul to interpret this - Jesus receives the Holy Spirit in the John the Baptist narratives in all four gospels, though he is not said to have been baptized by John in Luke or John.
2 Corinthians 2.14-15
2.14 But thanks be to God, who in [Christ] always leads us in triumph, and through us spreads the fragrance of the knowledge of him everywhere. 15 For we are the aroma of [Christ] to God among those who are being saved and among those who are perishing, 16 to one a fragrance from death to death, to the other a fragrance from life to life
Paul is using the metaphors of fragrance and aroma to describe the spread of the Christian message. The reason for this particular metaphor is that [Christ] is aromatic because the word means Anointed One and anointing oil is aromatic.
We find this in John 12.1-2:
John 12.1 Six days before the Passover, Jesus came to Bethany, where Laz′arus was, whom Jesus had raised from the dead. 2 There they made him a supper; Martha served, and Laz′arus was one of those at table with him. 3 Mary took a pound of costly ointment of pure nard and anointed the feet of Jesus and wiped his feet with her hair; and the house was filled with the fragrance of the ointment.
But the concept of an aromatic anointing goes back to the Old Testament, as in in Exodus 30.22-33:
Exodus 30:22 Moreover, the Lord said to Moses, 23 “Take the finest spices: of liquid myrrh five hundred shekels, and of sweet-smelling cinnamon half as much, that is, two hundred and fifty, and of aromatic cane two hundred and fifty, 24 and of cassia five hundred, according to the shekel of the sanctuary, and of olive oil a hin; 25 and you shall make of these a sacred anointing oil blended as by the perfumer; a holy anointing oil it shall be. 26 And you shall anoint with it the tent of meeting and the ark of the testimony, 27 and the table and all its utensils, and the lampstand and its utensils, and the altar of incense, 28 and the altar of burnt offering with all its utensils and the laver and its base; 29 you shall consecrate them, that they may be most holy; whatever touches them will become holy. 30 And you shall anoint Aaron and his sons, and consecrate them, that they may serve me as priests. 31 And you shall say to the people of Israel, ‘This shall be my holy anointing oil throughout your generations. 32 It shall not be poured upon the bodies of ordinary men, and you shall make no other like it in composition; it is holy, and it shall be holy to you. 33 Whoever compounds any like it or whoever puts any of it on an outsider shall be cut off from his people.’”
It's also found in the Song of Solomon:
Song of Solomon 1.3 your anointing oils are fragrant, your name is oil poured out;
Best,
Ken